Python: check if one regex covers another regex

Question

I'm attempting to check if one regex covers another regex in Python 2.7 .

For example, I have the following expression:

([a-z]+\.\d+(\.\d+)?)?

And I would like to know if it covers one of the following expressions:

([a-z]+\.[0-9])?         (covers)
([0-9]+\.\d+(\.\d+)?)?   (does not cover)
([a-z]|[0-9])?           (does not cover)

Is it possible to check if a regex covers another regex? And if possible, do you have suggestions how to implement this?